Biomass is recently produced organic matter which can be burnt as a fuel and falls into two main categories; woody biomass including forest products, untreated wood products and short rotation coppice, and non-woody biomass including animal waste, food processing waste and high energy crops. For small scale applications woody biomass is generally used, taking the form of wood pellets, chips and logs. Burning biomass can be considered carbon neutral, since the amount of CO2 released is equal to the amount that was absorbed by the plant during its growth.

The two main biomass heating systems are stand-alone stoves which may also have a back boiler to provide hot water, and boilers providing central heating and hot water. There are three main types of fuel supply, logs which must usually be loaded by hand, wood chips and wood pellets which can both be automatically loaded from a storage hopper. The automation of loading these burners means less hassle and mess. Wood pellets are a denser form of energy than wood chips and can therefore be stored in a smaller hopper.

Modern wood burning boilers have an efficiency of around 90%, a far cry from traditional open fires which have an efficiency of around 20%.

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